Unfortunately, native polyester fibers and plastics as manufactured generally have an undesirable yellow appearance. At present, in order to improve the apparent whiteness of polyester fibers or neutral color characteristics of polyester plastics, certain so-called toners are incorporated into the polyester to hide or neutralize the yellow color.
Cobalt acetate is one of the most widely used toners in the industry to mask the yellow color of polymers. However, cobalt acetate has a number of noteworthy disadvantages. For example, cobalt acetate toned materials tend to be unstable during storage and are particularly susceptible to temperature and humidity, and tends to undergo an undesirable color shift toward yellow. Further, when high cobalt concentrations are needed to mask the yellow color of some polymers there is a tendency to impart a gray color to the polymer.
Another disadvantage in the use of cobalt acetate is the limitation set by various governmental agencies in the level of cobalt deemed allowable in polyester catalyst systems.
Further, cobalt salts tend to lower the resulting polymer's thermal stability and increases acetaldehyde formation in poly(ethylene terephthalate).
Lastly, cobalt has a strong tendency to form insoluble residues in manufacturing process equipment, thereby leading to production problems.
U.S. Pat. No. 4,745,174, discloses certain 1-cyano-3H-dibenz[f,ij] isoquinoline-2,7-diones which are useful as organic toners for polyester fibers and plastics and which solve many of the aforementioned problems. These compounds, however, are expensive to manufacture and provide environmental, safety, and provide toxicological concerns relative to their manufacture and use.
Suitable toners for polyester must be non-extractable from the polymer to provide the greatest degree of safety. Also, they must be stable to sunlight and to a wide range of conditions of temperature and humidity. Further, they must not sublime or change hue as a result of the extremely high temperatures encountered during the polyester manufacture. In addition, the toner must have no adverse effects on the physical properties of the polyester polymer.
U.S. Pat. Nos. 3,488,195 and 3,849,139 disclose the use of certain 1,4-bis-(arylamino)anthraquinones including 1,4-bis(2,6-dialkylanilino) anthraquinones for blue tinting photographic X-ray film to aid in the examination of the X-ray patterns obtained therein for obtaining accurate diagnosis of complex radiographs. No mention that these blue compounds would be particularly efficacious in combination with certain red colorants as toners to overcome the inherent yellow characteristics of polyesters is made, however, in either patent.
U.S. Pat. No. 2,731,476 teaches the use of certain blue 1,4-bis(2,6-dialkylanilino) anthraquinone sulfonamide derivatives as dyestuffs and pigments for coloring lacquers and plastic masses.
Finally, U.S. Pat. Nos. 4,359,570; 4,403,092; 4,420,581; 4,790,581; 4,740,581; and 4,999,418 disclose colored polyester compositions containing varying levels of the blue and red colorants useful in the practice of this invention copolymerized therein; however, no mention is made in these patents regarding the potential utility of the disclosed compounds as components to produce an efficacious toner system for polyesters.